This invention relates to electroluminescent (EL) display panel devices and more particularly to such a device wherein the EL panel is readily replaceable.
It is highly desirable to provide a display device which comprises a housing having a thin-film EL panel mounted thereon. The housing contains a solid state memory and a micro-computer for controlling the transfer of data from the memory to operate the panel.
One of the problems of such a display device is that the EL panel therefor has a relatively short life and has to be replaced from time-to-time. A typical EL panel is formed by providing a first set of thin-film transparent electrodes on a glass substrate followed by thin-film layers of a first dielectric, a phosphor, a second dielectric, and a second set of thin-film electrodes positioned orthogonally to the first set. The first and second sets of electrodes thus form a crossed-grid array on the panel. A back glass cover plate for protecting the thin-film structure is then held on the substrate by a marginal seal of epoxy.
It should be appreciated that in a typical EL panel, the electrodes of each set spaced with a high linear resolution, on the order of fifty-six per inch. When using a one square inch EL panel, and providing for alternate electrodes of each set to terminate at opposite sides of the substrate, twenty-eight electrode terminals are provided along each of the four marginal sides of the panel. A panel suitable for use in the present invention is disclosed in the commonly assigned patent application of Sam H. Rustomji entitled "High Resolution Thin-Film Electroluminescent Panel" filed May 10, 1982, and bearing Ser. No. 376,572.
Since individual contact must be made by the electronic controls in the housing with each of the fifty-six electrodes in each set of electrodes on the panel, it is highly costly to provide discrete leads with bonded connections, for example, to each of the electrode terminals. Moreover, the crossed-grid array formed by the electrodes on the panel provides a large number of picture elements thereon, as many as 3136 in a square inch area. If even one of these picture elements goes out during the operation of the display device it is necessary to replace the panel. This necessitates not only the disconnecting of all one-hundred-twelve leads from the electrode terminals on the inoperable panel but the bonding of new leads to the electrode terminals on the new panel.
Another problem of such a display device is providing for protecting the phosphor layer on the panel from contact with moisture. Thus, if even a minute amount of moisture, such as inevitably present in the ambient air, works its way into the phosphor layer, through a pin hole, for example, in the thin-film structure, the picture element located at that point loses its ability to emit light when energized. It is thus desirable to provide an airtight enclosure for the thin-film structure and thus the phosphor layer on the panel. Accordingly, in the above referred to commonly assigned patent application, Ser. No. 376,572, a thin-film of alumina is sputtered over the back surface of the thin-film structure provided on the glass substrate. This thin-film of alumina is of great help in encapsulating, i.e., sealing the thin-film structure and preventing air from working its way, in time, into the phosphor layer. The marginal epoxy seal provided for the back glass cover plate also serves to help prevent ambient air from passing into the space above the thin-film structure on the substrate. However, these seals are not sufficiently airtight for this purpose resulting in the life of the phosphor layer and thereby the panel to be shortened.